Background: The etiology of isolated mediastinal lymphadenopathy (without lung involvement or peripheral lymph node enlargement) is difficult to approach. Though various methods are available for histopathological confirmation, few literatures are there regarding the etiological diagnosis of isolated mediastinal lymphadenopathy. Aims and objective: This study was taken up with the aim to investigate the pattern of involvement of isolated mediastinal lymphadenopathy and to analyze the etiology among the adult patients presenting to a tertiary care institution in Eastern India. Materials and methods: A total of 50 patients were subjected to our study. Non-invasive investigation such as x-ray, CT scan, mantoux test etc. were done and these investigations established only a indirect evidence of etiological diagnosis. For definitive diagnosis, fine needle aspiration biopsy cytology ( FNABC) or biopsy from peripheral lymph node( if any) or various invasive investigations such as CT guided biopsy from mediastinal lymph node, bronchoscopy with transbronchial biopsy, mediastinoscopy or endobronchial ultrasound-guided transbronchial needle aspiration were done wherever feasible. Results: Overall tubercular lymphadenopathy was the most common (45 among 50 patients; 90%) followed by sarcoidosis (3 among 50 patients; 6%), lymphoma (1 among 50 patients; 2%) and carcinoma of lung ( 1 among 50 patients; 2%). Conclusion: So tuberculosis is the leading cause of isolated mediastinal lymphadenopathy.